Relaxing on a bed of nails: an exploratory study of the effects on the autonomic, cardiovascular, and respiratory systems, and saliva cortisol

J Altern Complement Med. 2011 Jan;17(1):5-12. doi: 10.1089/acm.2010.0135. Epub 2011 Jan 5.


Objectives: This study investigated subjective and physiologic responses of lying on a bed of nails (BN) called the Shakti-mat and of listening to relaxing instructions and music. The BN has 6210 sharp-edge 5-mm plastic nails about 5 mm apart.

Design: Thirty-two (32) healthy participants went through four conditions in randomized orders combining BN and relaxing instructions.

Results: The subjective pain ratings on the BN increased immediately and reached a peak within 30 seconds. The pain then subsided gradually, indicating a habituation effect. Self-rated relaxation increased over time in all conditions. Systolic and diastolic blood pressures were higher, heart rate was slower, and there was more high-frequency power heart rate variability (HRV), and signs of increasing circulation in the back on the BN. The relaxation instruction especially affected breathing and the HRV-indices standard deviations of normal interbeat intervals and low-frequency power, both known to be responsive to slow breathing. There were no differences in saliva cortisol.

Conclusions: Healthy participants habituated to the induced pain on the BN and were able to subjectively relax. When on a BN, signs of both sympathetic and parasympathetic nervous system activity were observed. The pain may hypothetically have triggered a parasympathetic response.

Publication types

  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Affect / physiology*
  • Autonomic Nervous System / physiology*
  • Back / blood supply
  • Blood Pressure / physiology
  • Female
  • Habituation, Psychophysiologic / physiology*
  • Heart Rate / physiology
  • Humans
  • Hydrocortisone / metabolism
  • Male
  • Middle Aged
  • Music Therapy*
  • Pain Perception / physiology*
  • Pain* / physiopathology
  • Pain* / prevention & control
  • Pain* / psychology
  • Relaxation / physiology
  • Relaxation / psychology
  • Respiration
  • Saliva / chemistry
  • Skin Physiological Phenomena


  • Hydrocortisone